Magnetic Random Access Memory (MRAM) is an emerging technology that can provide an alternative to traditional data storage technologies such as hard disc drives, optical data storage media, RAM, DRAM, and FLASH memory, just to name a few. MRAM has desirable properties including fast access times like DRAM and high areal storage densities like hard disc drives. MRAM stores a bit of data (i.e. information) as an alterable orientation of magnetization in a patterned thin film magnetic element that is referred to as a data layer, a sense layer, a storage layer, or a data film. The data layer is designed so that it has two stable and distinct magnetic states that define a binary one (“1”) and a binary zero (“0”). Although the bit of data is stored in the data layer, many layers of carefully controlled magnetic and dielectric thin film materials are required to form a complete magnetic memory element. One prominent form of magnetic memory element is a spin tunneling device. The physics of spin tunneling is complex and good literature exists on the subject of spin tunneling.
In FIG. 1a, a prior magnetic tunnel junction device 401 includes a spacer layer 414 that separates a data layer 410 from a reference layer 412 (also referred to as a pinned layer). If the spacer layer 414 is made from a dielectric material (e.g. aluminum oxide Al2O3) then the device 401 is a tunneling magnetoresistance device (TMR). On the other hand, if the spacer layer 414 is made from an electrically conductive material (e.g. copper Cu), then the device 401 is a giant magnetoresistance device (GMR). The data layer 410 is made from a ferromagnetic material fm2, such as nickel-iron (NiFe), for example. The reference layer 412 is also made from a ferromagnetic material fm1, such as cobalt-iron (CoFe), for example. The reference layer 412 has a pinned orientation of magnetization m1, that is, the pinned orientation of magnetization m1 is fixed in a predetermined direction and does not rotate in response to an external magnetic field. In contrast, the data layer 410 has an alterable orientation of magnetization m2 that can rotate between two orientations in response to an external magnetic field.
As an example, in FIG. 1b, when the pinned orientation of magnetization m1 and the alterable orientation of magnetization m2 point in the same direction (i.e. they are parallel to each other) the data layer 410 stores a binary one (“1”). On the other hand, in FIG. 1c, when the pinned orientation of magnetization m1 and the alterable orientation of magnetization m2 point in opposite directions (i.e. they are anti-parallel to each other) the data layer 410 stores a binary zero (“0”).
In FIG. 2, a prior MRAM device 400 includes a plurality of the magnetic tunnel junction devices 401 arranged in an array (e.g. a cross-point array) and positioned at an intersection between a plurality of column conductors 407 and row conductors 405 that are in electrical communication with the data and references layers (410, 412). In order for the MRAM device 400 to have a data storage density on par with other established data storage devices, such as hard disc drives and semiconductor memories, it is necessary to pack as many of the devices 401 as is possible in the array. To that end, in FIG. 1b, an area a, of the data layer 410 is made as small as possible by making a width w and a length l of the data layer 410 as small as possible (i.e. a1=w*l). By reducing the area a1, an areal density of the MRAM device 400 is increased and the data storage density is increased. In FIG. 1d, because the layers of material in the magnetic tunnel junction device 401 are very thin (e.g. from about 30 Å to about 50 Å for the data layer 410), a volume v1 as defined by a nominal thickness t of the data layer 410 and the area a1 is also very small (i.e. v1=a1*t).
However, one disadvantage arises from the high storage densities that are required to compete with well established data storage technologies. Namely, super-paramagnetism related reversal of the alterable orientation of magnetization m2. The reversal is due to the volume v1 being small, which results in a small magnetic volume for the data layer 410. When the magnetic volume is small, the anisotropy energy that holds the alterable orientation of magnetization m2 in a stable state is also small. Consequently, thermal noise/temperature fluctuations can flip the alterable orientation of magnetization m2 resulting in corrupted data being stored in the data layer 410.
Moreover, in FIG. 2, another disadvantage arises during a write operation to the MRAM device 400. A write current lx flowing through the row conductor 405 and a write current ly flowing through the column conductor 407 generate magnetic fields Hy and Hx respectively. Those magnetic fields cooperatively interact with the data layer 410 of a selected magnetic tunnel junction device 401′ and flip the alterable orientation of magnetization m2 of the selected device 401′. However, those magnetic fields (Hy, Hx) also interact with adjacent magnetic tunnel junction devices 401 in the array. Consequently, the aforementioned small anisotropy energy can cause the alterable orientation of magnetization m2 of adjacent data layers 410 to flip due to stray magnetic fields, thereby corrupting the data stored in adjacent data layers 410.
Consequently, there is a need for a magnetic tunnel junction memory device that includes a data layer that is super-paramagnetically stable and the data is non-volatile and immune to data corruption caused by thermal noise, temperature fluctuations, and/or stray magnetic fields.